Iron and Manganese Containing Multi‐Walled Carbon Nanotubes as Electrocatalysts for the Oxygen Evolution Reaction ‐ Unravelling Influences on Activity and Stability

Regulating the thickness of the carbon coating layer in iron/carbon heterostructures to enhance the catalytic performance for oxygen evolution reaction

The exploration of high-performance electrocatalysts for the oxygen evolution reaction (OER) is crucial and urgent for the fast development of green and renewable hydrogen energy. Herein, an ultra-fast and energy-efficient preparation strategy (microwave-assisted rapid in-situ pyrolysis of organometallic compounds induced by carbon nanotube (CNT)) is developed to obtain iron/carbon (Fe/C) heterogeneous materials (Fe/Fe₃C particles wrapped by carbon coating layer). The thickness of the carbon coating layer can be adjusted by changing the content and form of carbon in the metal sources during the fast preparation process. Fe/Fe₃C-A@CNT using iron acetylacetonate as metal sources possesses unique Fe/C heterogeneous, small Fe/Fe₃C particles encapsulated by the thin carbon coating layer (1.77 nm), and obtains the optimal electron penetration effect. The electron penetration effect derives from the redistribution of charge between the surface carbon coating layer and inner Fe/Fe₃C nanoparticles efficiently improving both catalytic activity and stability. Therefore, Fe/Fe₃C-A@CNT shows efficient OER catalytic activity, just needing a low overpotential of 292 mV to reach a current density of 10 mA cm^-2, and long-lasting stability. More importantly, the unique control strategy for carbon thickness in this work provides more opportunity and perspective to prepare robust metal/carbon-based catalytic materials at the nanoscale.

Fabrication of manganese borate/iron carbide encapsulated in nitrogen and boron co-doped carbon nanowires as the accelerated alkaline full water splitting bi-functional electrocatalysts

With high prices of precious metals (such as platinum, iridium, and ruthenium) and transition metals (such as cobalt and nickel), the design of high-efficiency and low-cost non-precious-metal-based catalysts using iron (Fe) and manganese (Mn) metals for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are critical for commercial applications of water splitting devices. In the study, without using any template or surfactant, we successfully designed novel cross-linked manganese borate (Mn3(BO3)2) and iron carbide (Fe3C) embedded into boron (B) and nitrogen (N) co-doped three-dimensional (3D) hierarchically meso/macroporous carbon nanowires (denoted as FexMny@BN-PCFs). Electrochemical test results showed that the HER and OER catalytic activities of Fe1Mn1@BN-PCFs were close to those of 20 wt% Pt/C and RuO2. For full water splitting, (-) Fe1Mn1@BN-PCFs||Fe1Mn1@BN-PCF (+) cell achieved a current density of 10 mA cm-2 at a cell voltage of 1.622 V, which was 14.2 mV larger than that of (-) 20 wt% Pt/C||RuO2 (+) benchmark. The synergistic effect of 3D hierarchically meso/macroporous architectures, excellent charge transport capacity, and abundant active centers (cross-linked Mn3(BO3)2/Fe3C@BNC, BC3, pyridinic-N, MNC, and graphitic-N) enhanced the water splitting catalytic activity of Fe1Mn1@BN-PCFs. The (-) Fe1Mn1@BN-PCFs||Fe1Mn1@BN-PCF (+) cell exhibited excellent stability owing to the superior structural and chemical stabilities of 3D hierarchically porous Fe1Mn1@BN-PCFs.

Particle size-controlled synthesis of high-performance MnCo-based materials for alkaline OER at fluctuating potentials

Mn and Co containing nanocubes were produced by hydrothermal synthesis. The materials consist of metal spinels and carbonates, where spinels ensure high activity and carbonates contribute to high stability in the oxygen evolution reaction.